Radio selective alarm system with a central transmitter



Dec. 30, 1952 P. E. FISCHLER 9 RADIO SELECTIVE ALARM SYSTEM WITH A CENTRAL. TRANSMITTER Filed May 25, 1948 2 SHEETS-SHEET 1 j'fitcrm. Suzi rive Susc T/VE Snea-nve SELECTIVE SELECTIVE sun- 1v: Recs/wee RECEIVER RECEIVIZ RECEIVER ECI VEIZ Recs: v52 Recs/v52 600m 600m 600m GOO v 400- 400m 400 /0 l0 l0 l0 I C OMMUA/IT v 1 Comma/v17 v *2 H M 02 F M Tznusmrysa l2 "5 3 13? EBB/AZ? T Remy PANEL l cournol. MULTI 7on2 a I N M ICHROPHoA/E Guam TERNSM/fii.

, l EH67: Osman o2 l CENTRAL; y Loam/50 Teak/smrree Seusmve IZELRY 1N VEN TOR. PAUL E. F/SCHLER A T TORNEV Dec. 30, 1952 P. E. FISCHLER RADIO SELECTIVE ALARM SYSTEM WITH A CENTRAL TRANSMITTER 2 SHEETS-SHEET 2 Filed May 25, 1948 Queuing u2waGhN n20 Patented Dec. 30, 1952 RADIO SELECTIVE ALARM SYSTEM WITH A CENTRAL TRANSMITTER Paul E. Fischler, Avon, N. Y., assignor to Technical Alliance, Inc., a corporation of New York Application May 25, 1948, Serial No. 29,067 3 Claims. (01. 250-17) This invention relates to radio selective alarm systems with a central transmitter.

An object of the system is to provide a system particularly suited for use as a. fire alarm or first aid call system although it may be used for any other purpose for which it is adapted.

Another object is to provide a system of the class described wherein the operations necessary to broadcast air alarms are reduced to a minimum and wherein no preliminary adjustments, tuning or the like are necessary to instantly broadcast an alarm.

A further object is to provide a system of the class described wherein known types of transmitters and receivers may be used by the addition of certain auxiliary apparatus as hereinafter described.

Other objects and advantages will be apparent from the following specification wherein by way of illustration a preferred embodiment of the invention is disclosed. It will be understood, however, that what is herein described is merely by Way of illustration and is not limitative, as many modifications will be apparent to those skilled in the art. The invention is therefore as defined by the appended claims.

In the accompanying figures:

Figure 1 is a diagram of the invention as applied to a community fire alarm system;

Figure 2 is a diagram of the transmitter and control equipment used in the system shown in Figure 1; and

Figure 3 is a diagram of one of the receivers used in the system shown in Figure l. r

The invention will be described as applied to a rural or suburban fire alarm system serving two communities, but more than two communities or groups of receivers can be operate if desired.

Referring to Figure 1 the system comprises a plurality of receivers [0, H which all operate on the same RF carrier frequency. For the sake of illustration, in Figure 1 the receivers are assumed to be located in adjacent communities, those indicated by the numeral l operating with a 600 cycle modulation tone (frequency) superimposed on the carrier frequency of the transmitter l2, and those indicated at M on 400 cycles. Additional groups can easily be provided and each group selectively operated by a different tone frequency as hereinafter described.

The receivers N, H may be either AM or FM, depending upon the type of transmitter used and may be of any suitable construction. The system may operate in the UHF spectrum and the antennae used may be of the half-wave dipole type.

The output circuits of the receivers are modifie as hereinafter described.

The transmitter l2, of any suitable type to produce a RF carrier wave is provided with a multitone audio oscillator l3 to produce a plurality of modulation tones to modulate the carrier which may also be speech modulated. Control apparatus I4 is also provided all as hereinafter described.

sired receiver Ill or II (or all receivers tuned to the same RF frequency), the operator at the transmitter proceeds as follows:

One of the audio tone keys l5, l5a, l5b, is depressed for 10 or seconds. The carrier wave of transmitter I2 is thereby modulated with the de sired audio tone which is intercepted by all receivers. Only those receivers whose audio relays I6 are tuned to the transmitted audio frequency will be responsive to this signal.

During the period of tone aforesaid, the audio relay [6 in the selected receiver or group of receivers operates to energize relay 2| in said re-' ceiver or receivers to start. The time required for this sequence of operations at the receiver is approximately one second.

During this second, the speaker I! in the receiver is connected to the receiver output and operated by the broadcast audio tone and for the remaining time the key I5 is held depressedsay for 14 seconds-the speaker broadcasts an alert signal similar to the usual air-horn signal.

The operator new releases key [5 and depresses the microphone key Hi. The carrier current on the transmitter remains on when key [5 is released as presently described and is now speech modulated via the microphone l9 plugged into the jack and the operator verbally broadcasts any desired information.

When key I3 is released, the carrier is cut off the transmitter l2, thereby causing loss of voltage at the output 44 of receiver l 0 which de-energizes the sensitive relay 2| which opens the circuit to speaker I l and also restores the circuit 22 to audio relay It in preparation for the next call.

Detailed description of transmitter and control circuits Referring to Figure 2, while three tone keys [5, [5a, [5b are shown with their associated tone relays 25, 250i, 25b as the operation of all three control circuits is the same, only one will be described.

Actuation of the first key l5 closes its contacts 23 thereby closing the circuit 24 through tone.

relay 25 which, via its contacts 26 selects a resistance-capacitance network 27 which determines the frequency of the tone produced by the output of the oscillator I 3 connected to the audio or speech amplifier of transmitter ii at 28.

Contacts 29 of key I5 also (at the same time) close thecircuit 38 through the carrier hold-on relay 3| which locks itself in closed position via contacts 32 thereon across power supply circuit 33, 34.

Contacts 35 on hold-n relay 3! close to complete a circuit through plate supply relay .35 whose contacts 37 close to supply current via conductor 38 to the plate supply'circuit of transmitter l2 and the signal tone is-broadcast to the selected receiver Iii and heard via speaker ll therein.

After 10 or 15 seconds the operator releases key I and removes the modulating tone from transmitter I3 by releasing tone relay 25. However, by reason of the locking contacts 32 on the holdon relay 3! and contacts 3'! on plate suppiy relay 3d, the transmitter remains in operation to broadcast its un-modulated carrier wave, current being supplied to the plate supply primary therein via conductor 33.

If now the operator closes the normally'open microphone key [8 (the second to be used), the contacts Ida thereof close to complete a circuit through microphone relay 39 which opens its normally closed contacts it connected to the microphone speech input 2% to the transmitter, permitting the microphone is to operate to modulate the carrier current of transmitter 52 with speech. At the same time contacts it of this same relay 39 open to release the locking circuit (via contacts 32) of hold-on relay 3i. However, contacts Z of relay it close to maintain plate supply relay 33 closed, thereby keeping the plate supply current on conductor 33 to keep the transmitter in operation to broadcast.

Restoring the microphone key it to open circuit position releases relay at, closing contacts 5 and disabling the microphone it. This also opens contacts 32-, disabling relay 35, the contacts 3? of which disconnect the line voltage from plate supply 38 of the transmitter, thus stopping the broadcast. The neon lamp modulation indicator 55 may be mounted on panel Hi.

Detailed description of receivers and control circuits necessary for use with the system Referring to Figure 3- a radio receiver is shown in block form with its output circuit and the control circuit shown in detail.

The receiver proper as indicated within the dotted line 53 may be a conventional radio receiver of any suitable type having the plates P of its audio output connected to the output circuit is which in turn is connected to a series resonant circuit including condenser '55 and the winding of the audio relay it which may be of the type disclosed in the co-pending application, Serial Number 24,789, dated May 3rd, 1948.

As stated above, the receiver may be of any suitable type and no attempt has been made to show all of the circuits of same, the only modification necessary with many well known receiver circuits being the addition to the receiver of the parts shown in Fig. 3 outside the dotted line 43.

When the proper audio tone appears across 44, the resonant circuit is energized. This circuit serially includes contacts 46 on the sensitive relay 2|. When the audio relay it closes its contact 4 41, the carrier control circuit 48 of the receiver is connected to the input circuit 49 of the D. C. amplifier 59. This causes current to flow in the output circuit 5| of amplifier 59 and relay 2| is energized thereby.

Activation of relay 2| opens the circuit to audio relay It at contacts 46 and simultaneously the contacts 52 of relay 2! close to maintain the carrier control circuit 48, 49 closedto the amplifier 5! Contacts 53 of relay 2| also close to connect speaker I! through the 3 ohm winding 54 of the output transformer in receiver 43 to ground, so that the speaker operates as previously described to sound the tone signal broadcast from the transmitter;

Relay 2! remains locked in operated position as long as carrier energy is received by the re ceiver to provide a voltage from the receiver carrier control circuit 48 to the input 49 of the amplifier 50, as relay 2| is directly across the am.- plified output circuit 5|.

Thus, if the receivers are located at the homes of members of a volunteer fire department, this selective alarm system alerts the members and makes known to them the location of the fire without disturbing the community or causing trafiic congestion at the scene of the fire. In the event of first-aid calls, it permits the. members of the emergency squad to be summoned with maximum speed.

The system herein described can be installed at a minimum expense; no poles or wiresv are required. As all the firemen are called at once, and the general call repeated as often as necessary, much precious time can be saved as com, pared to calling individual firemen by telephone.

What is claimed is: i

1. In a system of the class described, av radio transmitter adapted to broadcast a carrier wave, a first :ey having normally open contacts, atone relay and a first circuit therefor including some of said contacts and a source of current for operating said relay, means for modulating the. carrier wave of said transmitter with an audio tone, means controlled by the operation of said relay for connecting said modulating means to said transmitter to broadcast the resultant Wave, a hold-on relay in said first circuit having contacts adapted to close the plate circuit of said transmitter, said hold-on relay having contacts in a second circuit serially including a plate supply relay and said current source, said hold-on relay having a locking contact whereby same is locked in operating position whereby said first key can be moved to open said first-mentioned contacts and both said relays remain energized to permit broadcasting of the unmodulated carrier wave, a second key having normally open contacts, a circuit serially including said last contacts and a microphone relay having contacts, a microphone having a circuit controlled by said last contacts, said microphone relay having contacts in circuit with the locking contacts of said holdon relay to release same while said microphone relay remains operated to permit speech modulation of the broadcast carrier current, said second key when restored to open circuit position opening said circuit to said microphone relay, thereby disabling said plate supply by releasing relay to stop the broadcast.

2. In a selective calling system of the class described, a tone frequency network including an oscillator and adapted to generate a' plurality of tones, manually controlled means ior 5818C:- tively switching saidhQtwork to obtain adcsircd tone including a tone relay, a key and a holdon relay controlled by said key, said hold-on relay having contacts operable to lock itself in circuit to hold said tone relay in operated condition, means controlled by said hold-on relay for connecting said network to a transmitter, a transmitter connected to said hold-on relay, said hold-0n relay having contacts controlling the transmitter plate supply circuit, a microphone, a microphone key for connecting said microphone and transmitter whereby said microphone may modulate the tone frequency of the transmitter, said last key, upon being restored to nonoperating position, terminating the broadcast, and means controlled by said microphone key for releasing said hold-on relay.

3. A radio transmitter including an amplifier and. a plurality of tone frequency networks, manually operated keys each having an operating position for connecting one of said networks to said transmitter to modulate the carrier Wave thereof and thereby broadcast a tone modulated signal, a hold-0n relay common to all said keys and operated by each of said keys to maintain said transmitter in carrier-current operation upon the release of any operated key to continue the broadcast of the carrier wave only, and manually controlled means for connecting a microphone to said transmitter to speech modulate said carrier wave subsequent to the release of any operated key, said hold-on relay being deenergized by the operation of said manually controlled means.

PAUL E. FISCHLE-R.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,476,093 Martin Dec. 4, 1923 1,863,829 Bruckel June 21, 1932 1,870,456 Inman Aug. 9, 1932 2,198,901 Boswau Apr. 30, 1940 2,214,101 Cumming Sept. 10, 1940 2,344,618 Koch Mar. 21, 1944 2,367,327 Beers Jan. 16, 1945 2,368,778 Purington Feb. 6, 1945 2,392,672 Koch Jan. 8, 1946 2,393,291 Clark Jan. 22, 1946 2,401,333 Bumstead June 4, 1946 2,415,727 Clare Feb. 11, 1947 2,446,279 Hammond Aug. 3, 1948 2,457,730 Roberts Dec. 28, 1948 2,480,115 Brown et al. Aug. 30, 1949 

